Tire testing systems which examine tires in order to determine the presence of any irregularities or nonuniformities are known in the art. Known systems typically move a tire to a testing station where it is engaged by some form of chuck apparatus and inflated to its normal pressure. The tire is rotated at a standard speed against a loadwheel. Data taken from load cells to which the loadwheel is attached is used to detect the presence of any irregularities which may have arisen during the manufacturing process. Additionally, the system typically measures the size of the irregularities and is equipped with devices for correcting the irregularities, for example, grinding devices which remove material from the tire.
It was an objective of prior art tire testing machines to provide proper positioning of the tire in the machine so as to facilitate accurate detection, measurement, and correction of any irregularities in the tire. As explained below, however, although prior art chuck apparatus have performed adequately in holding the tire during testing and correcting procedures, there remains room in the art for improvement.
One prior art chuck apparatus for use in a tire uniformity machine is disclosed in U.S. Pat. No. 4,023,407 and comprises an upper chuck and a lower chuck, each of which has a rim secured thereto for respectively engaging the upper and lower beads of the tire. The upper chuck is moved toward the lower chuck by a hydraulic cylinder to clamp the tire between the rims. The upper chuck includes a slidable plunger having a tapered nose that mates with a tapered recess formed in the lower chuck. A spring surrounds the plunger and is compressed upon moving the chucks together. The patent discloses that when the spring is fully compressed the chucks are in their closed and locked position. Thus, the force exerted by the spring is used to lock the tapered nose in the recess of the lower chuck.
Another prior art chuck apparatus for a tire testing machine is disclosed in U.S. Pat. No. 4,852,398 and includes a female member secured to an upper rim and a male member secured to a lower rim. The female member has a tapered recess that receives the nose cone of the male member, the lower male member being movable toward the female member by a hydraulic cylinder. A spring located within the male member biases the nose cone toward the recess. The hydraulic cylinder moves the entire male member toward the female member until the nose cone seats in the tapered recess, and the cylinder continues to move toward the female member which compresses the spring and increases the locking force exerted by the spring. The patent discloses that the spring force frictionally couples the nose cone to the tapered recess of the female member.
The prior art chuck apparatus discussed above perform the function of positioning a tire in a testing machine between rims carried by the upper and lower chuck members; however, such assemblies have drawbacks. For example, the distance that the one chuck member can be moved toward or away from the other chuck member is limited. Also, the use of springs in prior art chuck assemblies imposes limitations regarding the distance the one chuck member may be moved toward the other member and, in addition, affects the consistency of the forces applied to enhance locking together of the respective components.
Additionally, prior art chuck apparatus must use a spring which has a force constant and length that exerts the necessary force to lock the chuck members together. If the distance the chuck member is moved (i.e., its stroke length) is increased, then the length of the spring must also be increased in order to exert sufficient force against the chuck member over such distance. However, increasing the stroke length by a considerable amount would require a very large, complex spring capable of exerting force over the increased range of movement. Utilizing such a spring is neither practical nor economical. Thus, the distance over which one chuck member can be moved in prior art machines is constrained by the stiffness and length characteristics of the spring. In addition, in view of the fact that the force exerted by a spring varies as the length of the spring changes, the locking force exerted on prior art chuck members varies as the length of the spring changes. Consequently, prior art chuck apparatus typically do not apply a substantially constant force to lock and maintain the chuck members together.
Accordingly, there is a need in the art for an improved chuck apparatus which is free of the limitations of conventional apparatus, provides an increased stroke length in order to accommodate various size tires, and applies a substantially constant force to lock the chuck members together.